The stomach of many mammals and the large intestine of most mammals maintain indigenous flora which appear to function in a manner quite similar to those of the ruminant forestomach, i.e. conversion of both soluble and insoluble carbohydrate into volatile fatty acids (VFA), synthesis of microbial protein from crude protein or non-protein nitrogenous sources and synthesis of B vitamins. This would have considerable nutritional significance if the VFA, proteins and vitamins can be assimilated by the host and studies conducted in this laboratory present good evidence that significant amounts of VFA can be produced within and absorbed from the large intestine of the pony and pig. It also appears that significant quantities of microbial protein can be synthesized, digested and absorbed in some form by the large intestine of the pony. However, in addition to its nutritional importance, the production and absorption of VFA in the large intestine of the above species also appears to be intimately associated with the secretion and absorption of other electrolytes and water. This indication that the VFA also play a major role in the other functions of the large intestine is supported by evidence suggesting that excessive production of VFA in the large intestine can inhibit its motor activity and initiate diarrhea. This project would examine the general characteristics of digesta passage, VFA production and absorption and nitrogen utilization in the large intestine of a variety of species. It would also more closely examine the characteristics of large intestinal secretory and absorptive mechanisms by perfusion techniques and in vitro studies of isolated mucosa, to determine the mechanisms of and interrelationship between transport of inorganic ions, VFA and water.